Density baffle for clarifier tank

ABSTRACT

A baffle system for a clarifier tank where the tank has a tank bottom, a periphery and a substantially vertical peripheral wall bounding the interior of the tank, said tank having an effluent channel. The baffle system includes a plurality of baffles mounted on the clarifier tank, each baffle having a baffle surface with a lower end and an upper end. The upper end of the baffle surface is coupled to a wall of the clarifier tank, the lower end of the baffle surface is disposed at a substantially 60° angle away from the side wall of the clarifier tank such that the baffle surface slopes downwardly and away from the side wall.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/154,801, filed on Jul. 17, 2012 which is a continuation of U.S.patent application Ser. No. 12/512,489, which in turn is a C-I-P of U.S.patent application Ser. No. 12/423,181, filed on Apr. 14, 2009 whichclaims the benefit of U.S. Provisional Patent Application No.61/206,039, filed on Jan. 26, 2009; U.S. Provisional Patent ApplicationNo. 61/206,574, filed on Jan. 30, 2009; and U.S. Provisional PatentApplication No. 61/196,405, filed on Oct. 15, 2008, the entirety ofwhich are incorporated by reference.

BACKGROUND

1. Field of the Invention

This application relates to a baffle and baffle system for use in asolids-precipitating clarifier tank. More particularly, the applicationrelates to a baffle and baffle system having a plurality ofinter-engaged individual baffles secured to the clarifier tankperipheral wall.

2. Prior Art Discussion

Passive baffle devices, also known in the art as a lamella gravityseparators or settlers, are used in clarifier tanks for waste treatmentfor gravitationally separating suspended solids from solids containingcarrier liquid or fluid suspensions. The clarifier tanks, with whichsuch baffles are typically used, are circular or rectangularlyconfigured tanks in which a centrally mounted radially extending arm isslowly moved or rotated about the tank at or proximate the surface ofthe carrier liquid.

Specifically, in waste water treatment facilities utilizing secondaryclarifiers, the clarifier's effectiveness in removing solids is perhapsthe most important factor in establishing the final effluent quality ofthe facility. A major deterrent to effective removal is the presence ofsludge density currents which cause hydraulic short circuits within thetank. These short circuits, in turn, allow solids concentrations tounintentionally bypass the tank's clarification volume and enter theeffluent.

In the prior art, peripheral baffles are attached to the tank wall anddirected downward at an angle into the tank. These baffles help tointerrupt the density currents and properly redirect the flow of solidsaway from the effluent and into the main clarification volume (center)of the tank.

However, although these density baffle systems work to significantlyreduce solids from entering the effluent, under greater load conditionsthese baffle systems occasionally fail, allowing for the above describedshort circuits.

SUMMARY

The present arrangement overcomes the drawbacks associated with theprior art providing for a density current baffle and installationemploying the same, with an inclined surface, having a modified angle ofattachment, dimensioned to minimize the density currents and properlyredirect the flow of solids away from the effluent and into the mainclarification volume (center) of the tank.

To this end, a baffle system is used in a clarifier tank having a tankbottom and a periphery and a substantially vertical peripheral wallbounding the interior of the tank. The baffle system has a plurality ofbaffles mounted on the peripheral wall of the clarifier tank. Eachbaffle has a baffle surface with a lower end and an upper end. The upperend of the baffle surface is coupled to the side wall of the clarifiertank wall. The lower end of the baffle surface portion is disposed, at asubstantially 60° angle away from the side wall of the clarifier tanksuch that the baffle surface slopes downwardly and away from the sidewall.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be best understood through the followingdescription and accompanying drawings, wherein:

FIG. 1 shows a clarifier tank and density baffle in accordance with oneembodiment;

FIG. 2 shows the density baffle within a clarifier tank in cross sectionview, in accordance with one embodiment;

FIG. 3 shows a close up view of a density baffle surface from FIG. 1 inaccordance with one embodiment;

FIG. 4 shows a schematic diagram of the baffle of FIG. 1, in accordancewith one embodiment;

FIG. 5 shows a first set of exemplary test results;

FIG. 6 shows a second set of exemplary test results;

FIG. 7 shows a third set of exemplary test results;

FIGS. 8 and 8 b show a fourth set of exemplary test results;

FIG. 9 shows a fifth set of exemplary test results, in accordance withone embodiment;

FIG. 10 shows a sixth set of exemplary test results, in accordance withone embodiment;

FIG. 11 shows a seventh set of exemplary test results, in accordancewith one mbodiment;

FIG. 12 shows an alternative baffle surface, in accordance with oneembodiment; and

FIG. 13 shows an alternative baffle surface coupled to a tank, inaccordance with one embodiment.

DETAILED DESCRIPTION

In one arrangement, as shown in FIG. 1, a density current baffle 10 isshown attached to a tank wall T. Density baffle 10 is made from aplurality of connected baffle surfaces 12, each of which forming aportion of baffle 10 about the circumference of tank wall T.

Bracket elements 14 are positioned under baffle surfaces 12, preferablyat the connection points between adjacent baffle surfaces as shown inFIG. 1. In one arrangement, an upper mounting flange 18 is located atthe top edge of each of baffle surfaces 12 for coupling baffle surfaces12 to tank wall T. Also as shown in FIG. 1, an end flange 20 projectsdownward from each of baffle surfaces 12, substantially perpendicular totank wall T. Bracket element 14 and baffle surfaces 12 can be molded asan one piece fiberglass baffle.

FIG. 2 shows a cut away view of baffle 10 within a typically circulartype clarifier tank C, having an influent 1, tank wall T, a spillwayeffluent channel and a weir W. Sludge blanket S is shown at the bottomof clarifier tank C, referring to the settled solids.

In one embodiment, as shown in FIG. 3, a close up view is shown of asingle baffle surface 12 of baffle 10. As shown in FIG. 2, bafflesurface 12 may optionally have one or more vent openings 22 located atthe top surface. In one arrangement, vents 22 are formed as convexdeformations of upper mounting flange 18. As noted above, baffle 10 isconfigured to prevent solids carried by density currents from flowingupwards and out of the clarifier tank. However, because of the downwardsloping design of baffle surfaces 12, some solids may become trapped andproduce a buildup of gases damaging baffle surfaces 12 and possiblyreducing their functionality. Vents 22 allow these gases to escape tothe surface without harming baffle 10.

Using the basic design as set forth above for baffle 10 and bafflesurfaces 12, it has been found by the inventor that by implementingcertain advantageous arrangements of baffle surfaces 12, including thedeflection angle of baffle surfaces 12 from tank wall T, the length ofprojection of the bottom of baffle surfaces 12 from Tank wall T into thecenter of tank C and the position of baffle surfaces 12 at certainheights on tank wall T, the relative concentration of solids in theeffluent may be substantially reduced over the prior art designs. Thefollowing description sets forth the salient features of the baffle10/baffle surfaces 12 in those respects.

As shown in FIG. 4, the schematic drawing identifies the measurementsthat define the size and positioning of baffle surfaces 12.

-   -   D=distance from weir (water level)    -   L=Length of baffle surface 12    -   α=angle from wall T    -   t=size of end flange    -   P=Projection distance from wall T (based on α and L)

It is noted that the desired minimum horizontal projection is ideallybased on the following equation (s)

In metric units:

Minimum Horizontal Projection=440 mm+α(d−9.15) m,

-   -   Where Horizontal Projection is in millimeters    -   α=16.7 millimeters per meter, and    -   d=tank diameter in meters

Or in English Units

Minimum Horizontal Projection=18+α(d−30),

-   -   Where Horizontal Projection is in inches    -   α=0.2 inches per foot, and    -   d=tank diameter in feet

In some calculations—it is recommended to increase the minimumhorizontal projection by increasing the value of a to 0.3 inches/foot(25 mm/m).

In view of the above, an exemplary series or modeling tests wereperformed to simulate sample baffle (of similar basic design to baffle10 but with varying dimensions) performance in an exemplary 70-footdiameter clarifier C with 10-foot side water depth (height from bottomof tank to weir/water level). The dimensions of the exemplary clarifierC are given in the following Table 1.

TABLE 1 Circular Clarifier Dimensions Tank Diameter 70 ft Side WaterDepth 10 ft Bottom Slope 1:12 RAS Well Diameter  6 ft Inlet PipeDiameter  2 ft Influent Baffle Diameter 23 ft Influent Baffle HeightVariable Effluent Launder Type Outboard

Simulations data was conducted using no baffle, a prior art baffle andseveral alternative designs. The simulations are carried out for aperiod of 110 to 220 minutes (real-time). During this period of time,effluent solids concentrations and the calculated velocity field werecontinuously recorded.

In the present instance, seven different baffle configurations weredefined. Referring to FIG. 4 and Table 2 below, seven baffleconfigurations are set forth. Not identified in Table 2 is an eighthconfiguration, referred to as Case 0 which is a “no baffle” or baselineconfiguration.

Case 1 is a prior art design for a baffle for this size clarifier,namely a baffle with 45 degree inclination angle and a 26 inchhorizontal projection (18″+0.2 (70′−30′)=26″.

TABLE 2 Density Current Baffle Design Variations (Length dimensions areinches, angle measures are degrees) Case Number D L a P t 1 36.0 37.0 4526 3.0 2 36.0 52.4 30 26 3.0 3 12.0 37.0 45 26 3.0 4 36.0 48.0 45 34 3.05 36.0 24.0 45 17 3.0 6 60.0 37.0 45 26 3.0 7 36.0 30.3 60 26 3.0

In case 2, the inclination angle relative to wall T is a steep 30°,meaning it projects sharply downward. To maintain the projectiondistance P, the length L of the baffle surface was increased to 52.4inches.

In case 3, the standard prior art baffle of case 1 is positioned 1 footbelow the weir/water level instead of the typical 3 feet below as incase 1.

In case 4, the angle from tank wall T is kept at 45 degrees, but thebaffle's horizontal projection into the tank is increased by 8.″

In case 5, the angle from tank wall T is kept at 45 degrees, but thebaffle's horizontal projection is decreased by 8.″

In case 6, the prior art baffle of case 1 is positioned five feet belowthe weir instead of the normal three feet (of case 1).

In case 7, the inclination angle relative to wall T is a lowered to 60°,meaning it projects only slowly downward. To maintain the projectiondistance P (26″), the length L of the baffle surface was decreased to30.3 inches.

Using the above seven (plus blank—case 0) dimensions for the baffles,the simulations were run assuming a three foot (0.914 m) deep blanket(settled solids on the bottom of clarifier C) and a Surface OverflowRate (SOR) of 1300 gpd/sq ft (gallons per day per square foot of watersurface area). This high SOR value was selected to examine theeffectiveness of the baffles under what is generally considered a highflow rate or stress condition. While this is higher than typicalclarifiers operate in general, it insures that active density currentsare created and that the baffle designs are fully operating.

Computed effluent solids concentrations in the below test results areoutput for each Case scenario and normalized with respect to the maximumcarry-over concentration, calculated for the baseline (Case 0—No Baffle)computation. The test results are done on a “better than-worse than”basis, with the results being within the range of prior recorded “realworld” values and were consistent with one another and with theoperating conditions.

FIG. 5 shows a comparison of Cases 0-3 with relative effluent solidconcentration being measured over 110 minutes of operating time. FIG. 6shows a similar comparison of cases 0 and 4-7.

The results of Case 0 show that no baffle quickly results in a very highrelative effluent concentration. The prior art baffle arrangement ofCase 1 appears to do an effective job of reducing effluent solids underthese operating conditions.

Case 2, where the inclination angle relative to wall T is a steep 30°,appears to have some effectiveness, but the widely oscillating resultsshow that the steep angle likely creates an unsteady flow of solidspreventing the generating of constant reduced flow.

In Case 5, the angle from tank wall T is kept at 45 degrees, but thebaffle's horizontal projection is decreased by 8″. As seen from FIG. 6,this was only marginally effective at reducing solids in the effluent,but did not even achieve the same results as the prior art Case 1.

The Case 3 and Case 6 baffles were located one foot and five feet belowthe weir, respectively. As noted above, in the simulation, the clarifierC had a 10-foot side water depth and the sludge blanket was assumed tobe three feet deep from the bottom of clarifier C. Judging from theperformance of the Case 3 baffle, it may be concluded that it waspositioned too far from the blanket, while the wave-like variations inthe presentation of the Case 6 baffle results would appear to indicatethat it was positioned too close to the blanket. The findings of Cases 3and 6 confirm that baffles appears to be most effective when positionedmidway between the blanket and the launder channel so as to allowsufficient clearance for solids to be deflected without impacting theblanket or being drawn into the weir current.

Finally, it is noted that Case 4 baffle (45 degrees with extendedprojection), and the Case 7 baffle (60 degrees with basic 26″projection), were both effective at reducing the total suspended solidsin the effluent, at least as well, if not better than the prior art Case1.

In view of the above, another exemplary series or modeling tests wereperformed for Cases 1, 4 and 7 to simulate baffle performance in anexemplary 100-foot diameter clarifier C with 14-foot side water depth(height from bottom of tank to weir/water level). Boundary conditions inthe simulation were also maintained, including the influent solidsconcentration and the return flow compared to total flow.

In this testing, four sets of operating conditions were established,namely a low blanket with low flow, high blanket with low flow, lowblanket with high flow and high blanket with high flow.

In the operating conditions the low blanket and high blanket were 4.3feet and 6.3 feet, respectively. The low flow and high flow were definedas SOR=900 gpd/ft² and SOR=1200 gpd/ft², respectively.

Each of the three baffle configurations was scaled for the 100-footclarifier, as follows:

-   -   Case 01 (prior art): D=36.0 inches; L=45 inches; α=45°; P=32        inches (based on 18+0.2(100−30)); and t=3.0 inches    -   Case 04: D=36.0 inches; L=57 inches; α=45°; P=37.75 inches and        t=3.0 inches    -   Case 07: D=36.0 inches, L=37 inches, α=60°, P=32 inches and        t=3.0 inches

For the case where the sludge blanket was low, and the flow was lessthan SOR=700, vertical currents near the outer wall of the clarifier didnot form strongly. In fact, under these circumstances, these currentstend to rise up and then fall back on themselves. In this case, maximumeffluent solids concentrations are calculated during model spin-up(around t=40 minutes) and then they moderate somewhat. While it doesappear that maximum effluent solids concentrations are reduced withbaffles (cases 1, 4 and 7) in place, the influence of the baffles isminimized. The best performance is achieved for the Case 07 variation.The Case 7 has a basic horizontal projection, but the inclination anglefrom the wall is increased to 60 degrees. As a result, the end of thisbaffle design is positioned further above the sludge blanket than thestandard baffle.

FIG. 7 shows the results of the simulation with a high blanket and lowflow. Here, the difference between the low blanket and high blanket isonly 2 feet, and the top of the blanket is 2 feet closer to the baffle.As shown in FIG. 7, in this case it appears that the vertical currentswere stronger near the clarifier wall and the Case 0 effluent solidsconcentrations remained high even after model spin-up. In this samescenario, the Case 4 baffle configuration performed best. As before,however, in these low flow scenarios, the effectiveness of the bafflewas proportionally small.

In all of the low blanket simulations, particularly those with low flow,only weak density currents appeared at the outer wall of the clarifier,and those lacked sufficient energy to climb the wall and reach theeffluent trough. Later simulations showed that SOR in the range of 600to 800 gpd/sqft were required to produce short-circuiting currents.Blanket depth is also a contributing factor. This is consistent withfield results that suggest that at or below design flow, densitycurrents are not significant and the effect of the baffle is lessened.

Finally, a set of calculations was carried out for a high flow (1200SOR) condition with a high (6.3 foot) blanket. The results are shown inTable 3 below. In this scenario, the Case 01 and 07 baffles performedbest. From the flow patterns it appeared that the Case 4 baffle waspositioned too close to the blanket and created a disturbance there thataffected its performance.

TABLE 3 Percent Solids Reduction, High Flow-High Blanket RelativeEffluent Solids Concentration Case No. vs. Case 00 (%) 01 33% 04 63% 0730%The difference between Case 01, 04 and 07 baffles is the fact that theinclination angle of the Case 07 baffle (60° versus 45°) has been mademore shallow, in effect increasing the relative distance between thebaffle and the top of the sludge blanket. The calculated flow patternsin FIGS. 8A and 8B show the development of a short-circuiting pattern inthis area.

Based on the above test results, a third set of testing was done usingthe 100 foot (by 14 foot tall) clarifier arrangement using threesamples:

-   -   Case 8 (Prior art with 8″ projection extension) 45° inclination        angle and 32 inch horizontal projection.    -   Case 9 extended prior art baffle with 45° inclination angle with        39 inch horizontal projection (based on 18″+(0.3×(100−30))    -   Case 10 baffle 10 of the present arrangement having a        combination of a 60° inclination angle from wall T and an        extended 39 inch horizontal projection.

The flow patterns that resulted from these calculations are shown inFIGS. 9 and 10. The calculated relative solids concentrations show thatthe case 8 baffle, although effective was surpassed by the extendedbaffle (case 9−(20% more effective)) and even more so by the case 10,where baffle 10 exhibited, such as that shown in FIGS. 1-3, 30% moreeffective than the prior art baffle designs.

As such, the results in FIGS. 9 and 10 confirm that increasing thelength of the horizontal projection of baffle surfaces 12 improves theirability to deflect wider density currents. The width of the currentvaries with clarifier dimensions, solids settling characteristics, flowand other parameters. Moreover, simultaneously increasing theinclination angle to substantially 60 degrees raises the bottom of thebaffle, by end flange 20 further from the blanket which limits thesludge blanket's interference with the operation of baffle surface 12.

For example, this arrangement also opens a wider path for the solidsunder baffle 10 to be deflected from wall T. The flow patterns in FIG. 9indicate that the velocity vectors emerging from beneath baffle 10 arealigned horizontally, toward the center of the clarifier C, which keepshigher solids concentrations further from the effluent weir currents. Incontrast, the motion vectors at the top of both of the other baffles(Case 8 and 9) appear more vertically aligned. Accordingly, one featurethat is determinative of the effectiveness of baffle 10, is the velocityvector generated by the 60 degree angle as shown in case 10 of FIG. 9.In an alternative arrangement, the 60 degree angle can be lowered to 55degrees or increased to 70 degrees, so long as the velocity vector ofsolids can be aligned substantially horizontal to the clarifier tank. Asshown in FIG. 9 case 10 as compared to case 9 and case 8, the velocityvector of case 10 is closer to horizontal that either of the othercases.

Regarding the positioning of baffle 10 relative to the sludge blanket,the first test (70-foot clarifier diameter) implied that there is arange of suitable values. In that test, the clarifier C is 10 feet deepand the top of the blanket was at 3 feet. The Cases 1, 4 and 7 baffles,all of which performed relatively well, were mounted 3 feet below theweir, hut the bottom position of the 3 baffles were 19 inches, 11 inchesand 33 inches, respectively, above the blanket. Of the otherconfigurations, the Case 2 baffle was 3 inches above the blanket andapparently too close; the Case 6 baffle was into the blanket; the Case 3baffle, at 43 inches, appears to be too far from the blanket.

It is noted that the Case 5 baffle was 28 inches above the blanket,(within the distance range defined by Cases 1, 4 and 7), but it did notperform well. However, it is noted that the Case 5 baffle had a shorterhorizontal projection than the other baffles, and particularly shorterthat the present baffle 10. The Case 4 baffle, on the other hand, wasthe closest to the blanket of the three best performing test cases, at11 inches. Case 4 had the longest horizontal projection of all of thetest baffles. The case 7 baffle, at 33 inches, was almost twice as farfrom the blanket as the case 1 baffle (19 inches), and the two baffleshad the same horizontal projection, but the case 7 baffle had a 60degree inclination angle.

Accordingly, the test results show that the position of baffle 10 withinclarifier C relative to the top of the sludge blanket is not simply amatter of distance, but a combination of distance from the blanket aswell as inclination angle and horizontal projection. With the baffle 10having the dimensions as set forth above in Case 10 (60 degrees with 39inch projection) the best performance relative to the height of thesludge blanket (to the bottom of the baffle 10 at end flange 20) is 2feet + or −6 inches.

It is noted that the sludge blanket height is not always a definableposition as it is constantly changing in height based on the flow andsediment conditions within the clarifier. Thus, the optimum position forbaffle 10 is based on an estimate of typical blanket heights andvariations that might occur in normal operations in each particularclarifier C. In one arrangement, in order to address this issue, baffle10 may be positioned at a point midway between the average blanketheight and the weir in order to estimate the 2 foot from blanket height.

In any event, in the present arrangement, baffle 10, in order tofunction effectively across the range of operating conditions of anyclarifier C, is positioned at a low enough point that its proximity tothe blanket allows it to perform effectively whenever density currentscarrying solids are able to reach it, and not on low that there is adanger that the blanket could rise above it.

In an alternative arrangement, as shown in FIGS. 12 and 13, a bafflesurface 12 is shown with a modified bracket element 14. This bracketelement 14, extends backward to provide an additional mounting surfacebeyond the upper mounting flange 18. Such an arrangement, allows forbaffle surface 12 to be mounted directly below the effluent channelunder the weir.

In this arrangement, the substantially 60 degree angle is maintained.Also, the horizontal projection, as measured from the wall of theeffluent channel (instead of the tank wall) allows for additionalprojection of the lower end of baffle surface 12 into the center ofclarifier C. This positioning of baffle 10 directly below the effluentchannel, ensures a sufficient distance from the average height of thesludge blanket and ensures that the lower end of baffle surfaces 12 donot fall below the periodically rising sludge blanket.

In one arrangement, for typical twelve-fourteen foot deep clarifiers C,baffle 10 is optimally positioned five feet below the weir (waterlevel), which generally places it approximately midway between thetypical blanket and the launder channel.

As shown in FIG. 11, further calculations of solids concentrations inthe effluent are performed using the parameters of the third testcomparing these two baffle configurations (Case 8 prior art versus Case10 (baffle 10 of the present arrangement) over a broad range ofincreasing SOR values.

In order to further demonstrate the effectiveness of baffle 10 relativeto the prior art baffle arrangements, tests were again simulated witheven larger 130 diameter clarifiers C. In these cases, as with the abovedescribed samples in the third test, baffle 10 of the presentarrangement, with a 60 degree angle and extended horizontal projectionshows a 30% improvement in reduction in solids (in the effluent)relative to the model predictions based on prior art baffle designs. Ascan be expected, baffle 10 in the range of 55 to 70 degrees with asimilar extended horizontal projection, would achieve similar results tothe third test.

While only certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes orequivalents will now occur to those skilled in the art. It is therefore,to be understood that this application is intended to cover all suchmodifications and changes that fall within the true spirit of theinvention.

What is claimed is:
 1. A baffle system in a clarifier tank having a tankbottom, a periphery and a substantially vertical peripheral wallbounding the interior of the tank, said tank having an effluent channel,said baffle system comprising: a plurality of baffles mounted on theclarifier tank, each baffle comprising: a baffle surface, said bafflesurface having a lower end and an upper end, the upper end of saidbaffle surface being coupled to a wall of the clarifier tank, the lowerend of said baffle surface being disposed, at a substantially 60° angleaway from the side wall of the clarifier tank such that said bafflesurface slopes downwardly and away from the side wall.
 2. The bafflesystem of claim 1, wherein said baffle surfaces, further comprisemounting flanges for securing to said wall of said clarifier tank. 3.The baffle system of claim 2, wherein each of said baffle surfacesfurther comprise vent openings integrally molded within said mountingflange.